Adding extra spice to the Brumbies' Super Rugby Pacific derby on Saturday night, the NSW Waratahs coach says "a couple of good games" shouldn't suddenly make Meredith a Wallabies contender.
Yet clearly Wallabies coach Joe Schmidt believes the 26-year-old is.
"Having watched him at Brumbies training, he also is quite commanding in the way that he runs the team, in that others are looking for direction," Schmidt told Stan Sport last week after also gushing over the late bloomer's speed and versatility.
"Declan's done a longer apprenticeship than most coming into Super Rugby. Some of the other guys, they come in very young and it's hard to see the wood for the trees sometimes at 10, with that step up and pressure.
"And when you get to Test level, that wood's a lot thicker.
"Having had those experiences and built on them, I think it just allows him to see more, and stay calmer, and be more decisive."
Proving a worthy flyhalf replacement for Noah Lolesio following the ex-Wallaby's move to Japan, Meredith has steered the Brumbies to third on the ladder this season.
McKellar is not surprised, having been key to Meredith joining the ACT outfit in 2023.
"He's a good young man. Declan came down from Cairns and originally was probably a fullback that's developed into playing at 10," he said on Wednesday.
"He's performed well, performed well for them last year.
"I just get nervous for the individual when all of a sudden he's played a couple of good games, we start throwing in Wallaby chat again.
"Like, when are we going to learn that that sort of pressure on young men doesn't help them, and it's been going on for I don't know how many years now."
McKellar said he "could rattle off 10 names" of young playmakers whose careers have been cruelled after being over-hyped.
"You've got to string a couple of good seasons together before you develop, and we're just trying to find the diamond in the rough.
"Declan's been good, but I think as a game we need to not apply pressure on him and thinking that he's going to be the next big thing.
"Just let him continue to grow as a Super Rugby player to start with."
Increasing interest in Meredith comes after Schmidt used six flyhalves last year: Lolesio, Ben Donaldson, Tom Lynagh, James O'Connor, Tane Edmed and Hamish Stewart.
"I think we we're guilty of looking for quick fixes," McKellar said.
"That's not going to change what's been (happening) over a long, long period of time so I think we've got to just develop, get our system right, get our talent ID right.
"I'm not saying it isn't and it's certainly improved significantly but just be patient.
"Let players come through the system, develop over time and put them into the next level, whether it be go from colts to Shute Shield, or Shute Shield into Super Rugby, Super Aus and then obviously international rugby when they're ready."
McKellar pointed to his own five-eighth, 32-year-old Jack Debreczeni - who will start opposite Meredith on Friday night - as a prime example of a young No.10 who suffered from unfair expectations early in his career.
"Debs (played) the very first NRC (in 2014). He was the stand-out player and he got all this pressure put on him," McKellar said.
"He was going to be the next big thing. He was the next Steve Larkham because he happens to be 6-foot-3 as well and all that pressure was put on him and then he had some tough times.
"Over time, he's developed into now what is a very calm, steady influence. He thinks like a coach, Jack.
"If he makes a mistake now, he can flush it straight away.
"Whereas as a young player, he probably struggled with that and young players do struggle with that pressure and having to deal with pressure and stress throughout games."
